Background: Bupropion (BUP) has a potential to be an effective pharmacotherapy for
smoking cessation during pregnancy. Smoking during pregnancy stimulates placental carbonyl reductases
that catalyze the biotransformation of BUP. 4-methylnitrosamino-1-(3-pyridyl)-1-butanone
(NNK) is a potent carcinogen of cigarette smoke. Carbonyl reduction of NNK into 4-
methylnitrosamino-1-(3-pyridyl)-1-butanol (NNAL) constitutes a major step in NNK detoxification.
Thus, placentas of pregnant smokers on BUP therapy can become a site of drug-drug interaction.
Therefore, we investigated the effect of continuous exposure to BUP and cigarette smoke on the activity
of placental carbonyl reductases in the formation of NNAL from NNK.
Methods: The reductive metabolism of NNK was determined using microsomal and cytosolic subcellular
fractions of placentas obtained from non-smoking women treated with BUP for depression, and
women not exposed to BUP: non-smokers (control) and smokers. The effect of BUP and its metabolites
on the reductive metabolism of NNK was investigated using subcellular fractions of control placentas.
Results: The formation of NNAL from NNK by placental cytosolic fractions of heavy smokers (≥20
cigarettes per day) was lower than that of control (12.1±3.5 nmol.mgP-1 vs 16.5±6.0 nmol.mgP-1,
P<0.05). While being exposed to BUP, the activity of placental carbonyl reductases remained unaffected,
the formation of NNAL in the placental cytosolic fraction decreased only in the presence of
high concentrations of BUP metabolites.
Conclusion: Smoking during pregnancy decreases the detoxifying capacity of soluble carbonyl reductases
towards NNK. Given the experimental conditions, exposure to BUP and its metabolites should
not impede the reductive metabolism of NNK by placenta in vivo.